Diaphragm-less radioactive radiation counter

ABSTRACT

A radio-active radiation counter is provided with a counter chamber having a diaphragm-less open window, and two collecting electodes are disposed in said chamber and separated from each other. A gas to be ionized is injected in a pulse into the chamber intermittently to create a gas cloud for a short duration in the space where the electrodes are disposed, and a voltage pulse is applied across the electrodes during the presence of said gas cloud between the electrodes to operate the counter in order to measure the radiation coming into the chamber during the voltage being applied to the electrodes. Because of the absence of a diaphragm in the ray entrance window of the counter chamber, the absorption of radiation energy in a diaphragm is avoided and thereby it is possible to measure radiations of energy less than 1 Kev.

United States Patent 'Kawashima [151 3,678,274 [451 July 18,1972

[54] DIAPHRAGM-LESS RADIOACTIVE RADIATION COUNTER [72] Inventor:

[ 73] Assignee:

Nobuki Kawashima, Tokyo, Japan President of Tokyo University, Tokyo,Japan 221 Filed: March 20, 1970 21 App1.No.: 21,380

Primary Examiner-Archie R. Borchelt Attorney-Flynn & Frishauf ABSTRACT Aradio-active radiation counter is provided with a counter chamber havinga diaphragm-1ess open window, and two collecting electodes are disposedin said chamber and separated 30] Foreign n h Priority Data from eachother. A gas tobe ionized is injected in a pulse into I the chamberintermittently to create a gas cloud for a short 06!. 29, 1 969 Japan..44/8606l duration in the space where the electrodes are disposed and avoltage pulse is applied across the electrodes during the "2 presence ofsaid gas cloud between the electrodes to operate 58] f 6 R 83 i 5 D thecounter in order to measure the radiation coming into the 50/43 chamberduring the voltage being applied to the electrodes. Because of theabsence of a diaphragm in the ray entrance 1 window of the counterchamber, the absorption of radiation [-56] nefgrenges Cited energy in adiaphragm is avoided and thereby it is possible to UNITED STATES pATENTS measure radiations of energy less than 1 Kev. 2,924,715 2/1960l-lendee et a1. ..250/83.6 F1 X 5 Claims, 2 Drawing Figures Osc \jv t AQY DIAPHRAGM-LESS RADIOACTIVE RADIATION COUNTER BACKGROUND OF THEINVENTION of radioactive radiation in the field of, for example, nuclearphysics, radio isotope technology, etc.

As the field of research and application of radioactive radiationexpands, it has become necessary to develop a radiation counter for lowenergy radioactive radiations. Especially, as a result of the progressof the space science and technology, many radiation sources such asX-ray stars, pulsars etc. have been discovered in cosmic space, andthese radiation sources offer tremendous interesting material to spacephysicists. Therefore, it is natural to expect that a new phenomenawould be discovered in near future in the region of vacuum ultra violetray and soft X-ray, since these areas have not yet been extensivelyexploited due to the lack of good detectors for detecting such rays.

Some detectors have already been developed for measuring rays in thevacuum ultra violet region as an extension of the conventional opticalspectroscopic methods, but there is scarcely any detector for rays inthe soft X-ray region, and especially for soft X-rays of energy lessthan 1 Kev.

For a soft X-ray of energy range less than I Kev, the measurement shouldbe carried out under vacuum conditions by placing both the radiationsource and detector in a vacuum, since the soft X-rays tend to absorbinto the air. A conventional counter which has been used heretofore insuch a case as mentioned above has a gas chamber filled with a gas to beionized under pressure in a range of l 700 Torr and within whichcollecting electrodes are disposed, thus the ray entrance windowprovided in the chamber should be sealed by a diaphragm to support thepressure difference between the inside and outside of the chamber. Inthis construction of the counter, radiations entering into the chamberthrough the window are remarkably absorbed in the diaphragm which closesthe window, and this is the reason why the measurement of soft X-rays ofenergy less than I Kev is very difficult.

SUMMARY OF THE INVENTION The general object of this invention is toprovide a new radioactive radiation counter suitable for the measurementof soft X-rays and other radioactive radiations of energy less than IKev.

More specifically, the main object of this invention is to provide aradioactive radiation counter wherein the diaphragm is eliminated fromthe ray entrance window of the counter chamber and a gas to be ionizedis injected in a pulse into the chamber intermittently to create a gascloud for short duration between two collecting electrodes in order toperform effective ray counting operation.

These and other objects of this invention can be attained by providing acounter which comprises a chamber provided with a ray entrance window,two collecting electrodes disposed in said chamber and separated fromeach other and means to apply a voltage across said electrodes, whereinsaid window has no closing diaphragm in order to make the inside spaceof said chamber open to the outside vacuum space, a gas cloud is createdfor short duration in said chamber by injecting a gas to be ionizedintermittently into said chamber in pulse by means of a fast acting gasvalve and a pulse voltage is applied to said electrodes during thepresence of said gas cloud in the space between said electrodes andthereby the counter is operated to measure radiations coming into saidchamber. In the counter according to this invention a gas to be ionizedis provided in the chamber of the counter in a pulse, in orderv toeliminate a diaphragm which closes a ray entrance window of the counterchamber, and thereby to avoid the absorption and loss of radiationenergy in the diaphragm. Thus, the counter can work normally as acounter for a certain period of time without a diaphragm at the windowof the chamber.

More specifically, in a counter of this invention, a gas isintermittently injected in a pulse into a space between two collectingelectrodes disposed in the counter chamber having an open ray entrancewindow by using a fast-acting gas valve actuated by means of, forinstance, an electromagnetic coil, a mechanical hammer etc. and when thegas pressure in the space between the electrodes is built up to apredetermined value a voltage pulse as applied across said electrodes,thereby radiation coming into said chamber through the open window ismeasured during the time the voltage is applied to the electrodes.

Here, the timing of the application of a voltage pulse should beappropriately chosen so that the gas cloud is just existing in the apacebetween the electrodes and the gas has not yet diffused so much out ofthe chamber through the open window, in order to attain an effectiveoperation of the counter and to minimize the absorption and loss of theradiation energy caused by the gas at the outside of the counterchamber.

The foregoing and other novel features of this invention will now bedescribed in detail as applied to an illustrative embodiment, withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic crosssectional front view of an embodiment of a diaphragm-less radioactiveradiation counter according to this invention, and FIG. 2 is a partialview of the counter of FIG. 1 schematically illustrating a mechanicaloperator for the valve of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT A fast-acting gas valve whichcontrols the supply of a gas to a counter chamber 1 includes a valvemember 2 made of light metal such as aluminum etc. This valve member 2is disposed in a gas plenum 2 which communicates with said counterchamber 1 through an opening 4, and is normally pressed against thevalve seat around the opening by a spring 5 supported on one inner wallof the gas plenum 3. The valve member 2 and the valve seat are sealedhermetrically by a vacuum seal gasket 6 interposed therebetween. A gasto be ionized is supplied through a suitable gas inlet (not shown) andstored in the gas plenum 3 at pressure higher than the gas pressuredesired in the counter chamber for the operation of the counter. Whenthe valve member 2 is actuated intermittently at a high speed, the gasplenum 3 communicates with the counter chamber 1 though the opening 4,and the gas stored in the plenum is ejected into the chamber 1 and anappropriate gas density distribution is created in the chamber.

The valve member 2 is actuated by the excitation of an electromagneticcoil 7 mounted outside of the plenum 3 around the counter chamber 1. Theelectromagnetic coil 7 is excited instantaneously by the discharge of acapacitor 8 through a suitable switch 9 such as a thyratron. When thecapacitor 8 has a capacity of 200 pF and is charged to a terminalvoltage of 1,500 V and the inductance of the electromagnetic coil 7 isJ-l, a half period of the discharge of the capacitor 8 is about 200 S.In response to the excitation of the electromagnetic coil 7 by such adischarge of the capacitor 8 as mentioned above the valve member 2 isexpelled downward in the drawing at a high speed of more than 10 m/sec.The time required for the opening of a gap of 1 mm between the valvemember 2 and the valve seat is about 100 S, and the gas stored in theplenum 3 is ejected in a pulse through the opened gap and the opening 4into the counter chamber 1. When the gas pressure in the counter chamber1 is built up to a predetermined value a voltage pulse is applied acrosstwo electrodes and 11 disposed in the counter chamber 1 to operate thecounter and the radiation 12 coming into the chamber through an openwindow 13 of the chamber during the voltage being applied to theelectrodes is counted by the conventional method.

It is noted that the timing of the application of a pulse voltage to theelectrodes 10 and 11 should be appropriately chosen so that the gascloud is just existing in the space between the electrodes and the gashas not diffused so much out of the counter chamber 1 through the openwindow 13, in order to assure the efficient operation of the counter andto minimize the absorption and loss of the radiation energy caused bythe gas in the external space of the counter chamber The magnitude andthe pulse width of the pulse voltage to be applied to the electrodesstrongly depend on the gas pressure in the gas plenum and the timing atwhich the pulse voltage is applied to the electrode, as well as onwhether the counter is used as a proportional counter or a Geigercounter.

For example, when the gas is stored in the gas plenum 3 in aproportional counter according to this invention at the pressure of 1atm., and the timing of the voltage application to the electrodes 10 and11 is selected at a time 300 .S after the excitation of theelectromagnetic coil 7, the appropriate magnitude and pulse width of thepulse voltage to be applied to the electrodes 10 and 11 are 2 KV and 300.S,-respectively. If the counter is used as a Geiger counter, theparameters mentioned above can be chosen within much wider range.

Any gas selected from the gases used in the conventional counters suchas H Cl-l etc. can normally be used as a gas to be ionized for thecounter of this invention, while a gas having much lower ionizationpotential than that of gases mentioned above can also be used for thecounter of this invention which is operated in a pulse operation mode.

The repetition cycle of the gas ejection into the counter chamberstrongly depends on the pumping speed of the vacuum system whichevacuates the counter chamber and the vacuum space surrounding thecounter and on the capacity of a power supply in the charging circuit ofthe capacitor for exciting the electromagnetic coil, and it is possibleto choose cycles up to l0 C/S. However, in the case of choosing highercycle rates within the cycle range mentioned above, it is necessary toprovide a suitable cooling system to prevent overheating of theelectromagnetic coil.

Though the counting efficiency of the counter operating in pulseoperation mode according to the present invention is not so highcompared with that of a conventional counter of continuous operationmode, because of the pulse operation of the counter, the S/N ratio ofthe counter output can b increased by a suitable statistical treatment,and the advantage resulting from the increase of S/N ratio sufficientlycompensates for the disadvantage of rather low counting efficiency.

As a means to produce a gas cloud by ejecting a gas into a space betweenthe electrodes disposed in the counter chamber, means utilizing asupersonic shock wave, or a suitable pneumatic or hydraulic means canalso be used. It is also possible to use a mechanical chopper (see FIG.2).

It will be apparent to those skilled in the art that many modificatonscan be made by applying the principle of this invention to create a gascloud in a chamber having a diaphragm-less window by ejecting a gaspulse into said chamber and to operate said chamber as a diaphram-lesscounter. It is intended therefore to include within the scope of thisinvention all modifications and embodiments which retain the spirit ofthis invention.

lclaim:

1. A counter for measuring the intensity of energy of radioactiveradiations comprising:

a chamber provided with a diaphragm-less ray entrance window;

two collecting electrodes disposed in said chamber and separated fromeach other; a fast acting gas valve means rncludmg means for openingsaid valve means only for predetermined short periods of time forintermittently ejecting a pulse of gas to be ionized into said chamberto create a gas cloud in said chamber for a short duration; and

means for applying a pulse voltage to said electrodes during thepresence of said gas cloud in the chamber in the space between saidelectrodes, the counter being thereby operated for the measurement ofradioactive radiation of energy in a low energy region.

2. A counter according to claim 1 including a gas plenum, in which saidgas valve means is at least partially located, for storing said gas.

3. A counter according to claim 5, wherein said fast-acting gas valvemeans includes an electromagnetic gas valve.

4. A counter according to claim 5, wherein said fast-acting gas valvemeans includes a mechanical chopper valve means.

5. A counter according to claim 2, wherein said electromagnetic gasvalve is actuated by an electromagnetic coil connected in a dischargecircuit of a capacitor.

9 3 UNITED STA'ITES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3.678,274 Dated July 18 1972 Inventor(s) Nobuki KAWASHIMA It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Claims 3 and 4, line 1, change "5" to 1-;

Claim 5, line 1, change "2" to 3.

Signed and sealed this 6th day of February 1973.

(SEAL) Attest:

EDWARD M.FLE'I'CHER,JR. ROBERT GOTTSCHALK I Commissioner of PatentsAttesting Officer

1. A counter for measuring the intensity of energy of radioactiveradiations comprising: a chamber provided with a diaphragm-less rayentrance window; two collecting electrodes disposed in said chamber andseparated from each other; a fast acting gas valve means including meansfor opening said valve means only for predetermined short periods oftime for intermittently ejecting a pulse of gas to be ionized into saidchamber to create a gas cloud in said chamber for a short duration; andmeans for applying a pulse voltage to said electrodes during thepresence of said gas cloud in the chamber in the space between saidelectrodes, the counter being thereby operated for the measurement ofradioactive radiation of energy in a low energy region.
 2. A counteraccording to claim 1 including a gas plenum, in which said gas valvemeans is at least partially located, for storing said gas.
 3. A counteraccording to claim 5, wherein said fast-acting gas valve means includesan electromagnetic gas valve.
 4. A counter according to claim 5, whereinsaid fast-acting gas valve means includes a mechanical chopper valvemeans.
 5. A counter according to claim 2, wherein said electromagneticgas valve is actuated by an electromagnetic coil connected in adischarge circuit of a capacitor.